The present invention relates to an electronic control circuit for controlling an electromagnetic valve having an armature, in particular for a heating and/or air-conditioning system in a motor vehicle, having an electronic switching element in series with the coil of the valve.
International Patent Publication No. WO 94/19810 describes a control circuit for a solenoid valve which varies the driving current of the solenoid valve over time when the solenoid valve is to be brought from a flow-through position to a closed position. This is done because the driving current of the valve is reduced (but not to zero) so that the solenoid valve drops. Immediately thereafter, the driving current is increased again, but the current value remains below a value at which the solenoid valve is moved into its closed position. Consequently, the control circuit controls the driving current during the shut-down phase.
Conventional solenoid valves can be operated with a square-wave pulse-like driving current. In other words, the excitation of the solenoid is switched either off or on, and it is at the maximum when switched on.
In addition, it is known that the driving current for the coil excitation can first be controlled at an elevated value at the start of the pulse, with the coil excitation being returned to a nominal value at which the armature remains in a holding position (after a spring-loaded armature has overcome the first spring forces and adhesive friction).
One disadvantage of the conventional solenoid valves is that they produce relatively loud switching noises in closing when the armature and/or the valve strikes a stop in closing. If the valve is used to control an air-conditioning system in a motor vehicle, for example, the switching noises will be disturbing especially in slow driving and when the vehicle is standing still, because then the engine and driving noises are low.
An electronic control circuit according to the present invention for controlling an electromagnetic valve having an armature, in particular for a heating and/or air-conditioning system in a motor vehicle, having an electronic switching element in series with the coil of the valve offers the advantage compared to the related art that the switching element controls the valve voltage (or the valve current) applied to the coil so that the valve voltage reaches a first value when the valve is switched on; then the valve voltage is reduced to a second value which is lower than the first value, and thereafter the valve voltage assumes a third value which is greater than the second value and represents a holding voltage for holding the armature in its switched-on position. Due to the fact that the electromagnetic valve is first operated at a first value of the valve voltage, the armature is first accelerated to the extent that the initial spring forces and the adhesive friction are overcome. The armature thus set in motion then experiences a reduced acceleration due to the reduced electromagnetic energy, because the second value of the valve voltage is lower than the first value, but the second value is preferably selected so that the armature essentially maintains its speed. In the course of the remaining switch-on operation, the valve voltage assumes a third value which is greater than the second value, so that the armature of the valve enters the end position in a very short period of time despite the previous reduction in voltage from the first value to the second value. Furthermore, this yields the advantage that the armature striking the end stop is not associated with the loud impact noise mentioned in the related art, because the voltage and current program according to the present invention permits rapid switching while nevertheless preventing an excessive speed on impact with the end stop.
According to the present invention, the first value of the valve voltage or the valve current is in the form of a switch-on pulse, with the amplitude of the switch-on pulse being greater than half the nominal value. The period of the switch-on pulse amounts to approximately 0.1 to 0.6 times the valve switching time with abrupt excitation of the valve with a voltage higher than the holding voltage. As an alternative, the switch-on pulse may be composed of multiple successive pulses.
In addition, the second value of the valve voltage or valve current forms an initial value for a switch-on ramp. The second value amounts to a maximum of 0.8 times the nominal value of the valve voltage and/or valve current. After the valve voltage and/or valve current has been reduced from the first value to the second value, the switch-on pulse is followed by a voltage and/or current characteristic having a linear rise. As an alternative, the rise of the switch-on ramp may be nonlinear, preferably progressive or degressive. From this it can be deduced that the electromagnetic valve is operated with a magnetic energy that is reduced but is specifically controlled to increase during the switch-on ramp, so the acceleration of the armature is reduced.
In addition, it is provided in a preferred embodiment that the switch-on pulse is followed by a xe2x80x9cdead timexe2x80x9d during which the valve voltage and/or valve current is kept constant at the second value so that ramping of the switch-on ramp is delayed.
The end value of the switch-on ramp preferably forms the third value, with the third value corresponding in particular to the nominal value of the valve voltage and/or the valve current. The third value has a level at least corresponding to the holding voltage of the armature in its switched-on position. The valve voltage and/or valve current is kept constant for a period of time during which the valve is in the closed position. This period of time can be varied as needed.
To shut down the valve, the valve voltage and/or valve current is reduced abruptly, namely to a value between the third value and the voltage-free state. In another embodiment of the present invention, this value at the same time forms an initial value of a shut-down ramp. During the shut-down ramp, the valve voltage and/or valve current drops linearly to zero. As an alternative, the characteristic of the shut-down ramp may have a nonlinear decline, i.e., it may be progressive or degressive in particular. The duration of the shut-down ramp is determined by a coil free-wheeling diode, for example, connected in parallel to the coil.
In another embodiment, the individual control segments (switch-on pulse, dead time, switch-on ramp, switched-on position and shut-down ramp) are not determined by fixedly preselected conditions, but instead by the fact that instantaneous parameters of state determine the amplitude and/or the duration of at least one control segment. In a motor vehicle, for example, such parameters of state include the battery voltage, the rpm of a water pump in a combustion engine, the fluid pressure of a water circuit for an air-conditioning system and the coil temperature. In addition, it is necessary to detect the parameters of state by using suitable sensors. For example, a thermocouple may be provided to detect the coil temperature.
In addition, the level of the switch-on pulse, i.e., the level of the first value, is preferably adjusted to a desired level by the electronic switching element independently of the power supply voltage (for example, this may be the vehicle electric system, i.e., the battery voltage) of the electronic control circuit. This is important in particular when the battery voltage is not constant because of external influences, e.g., the outside temperature, because then reproducible switch-on operations are always achieved nevertheless.
Furthermore, the duration of the switch-on pulses is automatically adjustable in particular. The duration of the switch-on pulse depends on the position of the armature. The position of the armature is derived from the characteristic of the valve voltage and/or valve current by using a suitable electronic circuit which can be assigned to the electronic control circuit.
In another embodiment, an analyzing device is allocated to the electronic control circuit. This allocation includes not only providing information between them but also the spatial arrangement relative to one another. In particular, the analyzing device is part of the electronic control circuit.
At the start of the switch-on operation of the valve, the analyzing device determines from the rate of increase in the valve voltage and/or valve current a time at which the valve current will assume a plateau value which is below the holding current of the armature and at which the rate of increase in the valve current is zero or approximately zero. The rise in the valve current in this time range corresponds to the switch-on pulse mentioned in the preamble, but the valve current rise is preferably nonlinear (as a function of the inductance of the coil). In addition, the characteristic of the valve current and/or valve voltage is first determined during a switch-on operation when the valve is influenced by no interference quantities or only by those of a known value. This characteristic corresponds to a setpoint curve from which the slope is determined at any desired time, so that with a deviating characteristic (from which a deviating slope also follows) of the valve current and/or valve voltage, inferences can be drawn regarding the conditions under which the valve operates. If interference quantities act on the valve or emanate from the valve itself, the characteristic and the rate of increase of the valve current and/or valve voltage also change. Therefore, on the basis of a comparison between the setpoint curve and the characteristic of the valve current and/or valve voltage, it is possible to draw a conclusion regarding the extent of the acting interference quantity (quantities), so that the characteristic of the valve current and/or valve voltage can be adapted to the set-point curve by the electronic circuit. As an alternative, individual values of the setpoint curve may be determined at definable times. Values for the valve current and/or valve voltage which are determined in an operating-related switch-on operation and deviate because of acting interference quantities provide information regarding the amount of the acting interference quantity or quantities by direct comparison with the values determined for the setpoint curve. Consequently, adaptation of the characteristic of the valve current and/or valve voltage to the setpoint curve is also possible here in an advantageous manner. Both variants described above permit reliable closing of the valve in a sufficiently short period of time for various operating conditions, with optimum noise reduction also being achieved.
There is at least one interference quantity with each control operation or regulating operation. In the present case, there are several interference quantities, which will be discussed in greater detail below. If the coil is driven for a switch-on operation, an electromagnetic field that acts on the armature develops, thus setting it in motion. At the same time, the armature in its movement acts on a valve unit which should close the circuit of the heating and/or cooling water circuit. The water pressure in the medium circuit counteracts the valve unit and thus the armature which in turn counteracts the electromagnetic force created by the coil. Thus an interference quantity occurs at the valve unit, acting indirectly on the coil by way of the armature. Furthermore, the armature itself generates another interference quantity, namely due to friction in its mechanical guidance and/or due to the fact that the motion of the armature is attenuated by a spring, for example. Another interference quantity acts on the coil and is composed of an electric coil resistance that can be varied as a function of the coil temperature due to the change in the magnetic circuit produced by the movement of the armature (the armature is moved out of the coil) and due to the resulting change in the valve current. Finally, a voltage is induced by the movement of the armature in the coil and produces a current opposite the valve current. Due to these internal and external influences, the valve current and/or valve voltage does not increase in a valve switch-on operation according to the setpoint curve, but instead it increases in deviation from the latter. This deviation can preferably be detected by the analyzing device, which relays information regarding the interference quantities acting on the valve to the electronic control circuit, so the characteristic of the valve current and/or valve voltage can be adapted to the setpoint curve. In this way, a valve closing operation with reduced noise is made possible in a sufficiently short period of time in an advantageous manner.
In deviation from the preceding description, the setpoint curve of the valve current and/or valve voltage is not determined by a valve switch-on operation which is not influenced by any interference quantities or only by those of a known extent, but instead, in one variant, it is of course also possible to determine the setpoint curve on the basis of a simulation and/or a (laboratory) experiment. The values thus determined are used as standard values and can be stored in the analyzing device in particular.
Finally, the analyzing device preferably determines control parameters for influencing the characteristic of the valve current and/or valve voltage of a later time range from the rate of increase and/or from individual values of the valve current and/or valve voltage from the switch-on time of the valve until the time of reaching the plateau value as a function of the interference quantities acting on the valve. Furthermore, a prediction regarding the total valve closing time to be expected is possible from the initial characteristic of the valve control signal. For example, if the predicted total closing time is too long on the basis of a high water pressure, the electronic control circuit can increase the valve current and/or valve voltage so that the armature is accelerated to a greater extent, thereby yielding a shorter closing time in comparison with the total expected closing time. On the other hand, however, it is also possible to briefly turn off the valve current and/or valve voltage when a predicted total closing time is too short, resulting from a high speed of the armature, so that the speed of the armature is thereby reduced, yielding here again an optimum closing operation with reduced noise.